Inductive components are commonly fabricated using ferromagnetic cores and windings of insulated electrical wire. The ferromagnetic cores are typically toroidal cores, rod cores, or assemblies made of a lower E shaped ferromagnetic part and a ferromagnetic cap connecting the three legs of the E such as shown in FIG. 1.
The toroid and rod cores are manually or automatically wound with the insulated copper wire to form a number of multiple turn windings for a transformer or a single winding for an inductor. The assembly is then typically encapsulated to protect the wires. The circuit connection is made by the solder termination of the wires as required by the application. This approach has high labor costs because of individual part handling. It has large variability in electronic parameters such as leakage inductance, distributed and interwinding capacitance, and common mode imbalance between windings because of the difficulty in exact placement of the copper wires.
The E shaped and encompassing cap assembly of FIG. 1 is made into an inductive component by manually or automatically winding copper insulated wires around the legs of the E as required. Either gluing or clamping the cap in place and final encapsulation completes this subassembly. Similarly, the circuit connection is made by means of solder termination of the wires as required by the application. Not only does this device have the limitations of the toroid and rod core, as mentioned above, but also it generally is a much larger device. Because the cap is a separate device the magnetic paths have a resistance of non-ferromagnetic gaps between the E and the cap reducing the efficiency of the transformer.
Power transformers constructed as shown in FIG. 1 have the further disadvantage that the heat resulting from the resistance losses in the windings is not easily dissipated because the E core and cap isolate these windings from a heat sink.